looking at the info supplied i would say you have two problems the first is your timings 2.5-3-3-7 2T you need to change to T1 instead of T2 if that is possible on that mobo the second is you are not running in duel channel mode make sure your memory sticks are in either both of the green slots or both of the purple slots not one in green and one in purple making these changes should double your bandwidth.

okay, i see three probs here if you are using two 512meg sticks.
First your not running dual channel. second you are running 2t, should be 1t and third your memory is running at 333 Mhz not at 400 Mhz.
Go to your mem settings and either configure it manually or let it read from the SPD. You may need to move one of the modules to a different slot on the mother board to run dual channel, check the layout in your mother board manual.